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Understanding melt penetration in ophiolites is important in revealing the formation and evolution of the oceanic lithosphere, as well as the formation of chromite deposits. We conducted in situ Li isotope analysis of olivine grains from the harzburgite, podiform chromitite and dunite envelope of the mantle sequence, and dunite and wehrlite cumulates from the crustal sequence of the Pozantı-Karsantı ophiolite. Olivine in the different rocks has variable and distinctive Li concentrations (0·95 to 2·01 ppm) and δ⁷Li isotopic compositions (-5·43 to 16·65 ‰). The olivine in the refractory harzburgite of the Pozantı-Karsantı ophiolite extends from MOR–peridotite-like compositions to lower δ⁷Li values and higher Li concentrations, suggesting ingressive Li diffusion via melt penetration. The Li isotopic compositions of the olivine in the dunite envelope and podiform chromitite represent the compositions of their parental …